ABSTRACT Cocaine abuse and dependence are global problems with serious medical and social consequences. Cocaine is estimated to be the second most common illegal substance of abuse in the US and in Europe, with 1.5 million adult addicts in the US alone. There are currently no available treatments specifically approved for cocaine overdose, facilitation of abstinence, or reduction of relapse in addicts who have achieved abstinence. Most pharmacological medications used in in- patient addiction treatment rehabs are indicated for other conditions and are associated with poor tolerability. Behavioral therapies may not show long-term benefit, with loss in efficacy over time. Many pharmacological studies demonstrate the Orexin system, found in the brain, to have an important role in addiction, with the Orexin-1 Receptor (OX1R) having a specific primary role. An OX1R-derived mechanism could deliver a treatment paradigm shift from poorly tolerated symptom-relieving medications to effective, long-term reversal, with the potential for (i) smooth withdrawal in cocaine addicts, and (ii) reduction in the high rates of relapse in addicts who have achieved withdrawal. Therefore, OX1R antagonists represent a new mechanism for the treatment of craving and/or prevention of relapse in cocaine addiction. In the present application, C4X Discovery proposes to further develop an oral Orexin-1 receptor antagonist, C4X_3256, as a novel treatment for cocaine addiction, by reducing substance craving. Our preliminary data demonstrate C4X_3256 is a highly potent and selective OX1R antagonist, with long residence time at the receptor, good oral bioavailability, an excellent safety profile, and evidence of preclinical efficacy. In Specific Aim #1 we will evaluate C4X_3256's efficacy in reducing the positive reinforcing effect of cocaine in rats that exhibit robust, stable levels of cocaine self-administration, and also assess efficacy in drug and cue-induced reinstatement of cocaine to determine C4X_3256's ability to prevent relapse. In Specific Aim #2 we propose to perform radiolabeled ADME studies to evaluate the distribution, metabolism and excretion of C4X_3256, as well as safety pharmacology studies, an in vivo genetic toxicology study, and 28 day GLP toxicology studies. These studies will confirm that C4X_3256 has a suitable efficacy and safety profile for progression to a Phase I clinical trial in healthy volunteers. Specific Aim #3 will extend the toxicology studies for C4X_3256 by first manufacturing GMP compound, then testing C4X_3256 for reproductive safety so that further clinical trials can be conducted in both male and female patients. Additionally, we will extend the GLP toxicology studies in two species to 13 weeks. At the conclusion of this project, we will be able to progress C4X_3256 into a Phase IIa clinical trial of up to 3 months duration to test efficacy of this novel therapy in patients with cocaine addiction.